Ensuring quality measurements with the hackAIR sensing toolkit

With hackAIR, you can contribute to better information about air quality in your neighbourhood using a number of different tools. But how good are our data? What can we really say about air quality?

The general principle: official data as a foundation

To calculate the overall air quality map for a city, hackAIR supplements official air quality measurements with user-generated data. The outcome is a continuous map of estimated air quality. Similar to the weather report, we calculate probabilities and estimates for locations in which there are no official measurements. As our models are based on reference measurements, these will always dominate in case they contradict with user-generated data.

When you zoom in to a neighbourhood, you will see the individual measurements that have contributed to the overall estimate – both from official data and other sources.

Sky images to estimate air quality

When you take a picture of the sky, the specific shade of blue you see will vary depending on the air pollution. Using this principle, hackAIR calculates the so-called aerosol optical depth of publicly available and user-submitted images to estimate air quality, taking into account the specific location and time at which the picture was taken. Unfortunately, it is impossible to directly compare these measurements to exact PM10 or PM2.5 values. Instead, the hackAIR app is showing pollution categories (from bad to very good).

  • We mapped the air quality in Thessaloniki using sky photos and we compared these estimations with official measurements in the city. According to the results, our method is able to characterize the aerosol variability within urban centres and identify hotspots.
  • We are currently organising campaigns where we collect a quite big number of sky images taken from different devices so that we examine how the type of the camera affects the quality of the results.

Open hardware sensors

Testing the hackAIR sensors

Both hackAIR open hardware devices use the same component for air quality measurements: The SDS011 sensor. Generally, this component is seen as “the best sensor in terms of accuracy ” for low-cost electronics thanks to its larger fan and laser-based design. However, this does not mean the sensor is as accurate as official reference stations. A scientific evaluation of the SDS011  concluded that measurements are comparable for average humidity – high humidity and temperatures can cause less accurate measurements. The second version of the hackAIR home sensor will thus include a temperature and humidity sensor so that we can balance this effect.

  • The manufacturer of SDS011 sensor, Nova Fitness Co. Ltd., reassured us that the sensor is factory calibrated
  • We have placed some hackAIR sensing devices next to official stations and we are comparing their results.
  • We are testing the validity of the hackAIR sensing devices in laboratories using the Dylos Air Quality monitor.
Posted by / October 26, 2017